- (void)viewDidLoad{    [super viewDidLoad];    // Do any additional setup after loading the view.        _timeBtn = [UIButton buttonWithType:UIButtonTypeCustom];    [_timeBtn setBackgroundImage:[UIImage imageNamed:@"short2_apply_btn_disable"] forState:UIControlStateNormal];    [_timeBtn setBackgroundImage:[UIImage imageNamed:@"short2_apply_btn_over"] forState:UIControlStateHighlighted];    [_timeBtn setTitle:@"发送验证码" forState:UIControlStateNormal];    _timeBtn.frame = CGRectMake(100, 100, 150, 30);    [_timeBtn addTarget:self action:@selector(starTime) forControlEvents:UIControlEventTouchUpInside];    [self.view addSubview:_timeBtn];}- (void)starTime{    __block NSInteger timeout = 60; // 倒计时时间    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);    dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);        dispatch_source_set_timer(timer, DISPATCH_TIME_NOW, 1 * NSEC_PER_SEC, 0 * NSEC_PER_SEC);    dispatch_source_set_event_handler(timer, ^{        if (timeout <= 0 ) {            dispatch_source_cancel(timer);            dispatch_async(dispatch_get_main_queue(), ^{                [_timeBtn setTitle:@"发送验证码" forState:UIControlStateNormal];                _timeBtn.userInteractionEnabled = YES;            });        }else{            NSInteger seconds = timeout % 60;            NSString *strTime = [NSString stringWithFormat:@"%.2d",seconds];            dispatch_async(dispatch_get_main_queue(), ^{                NSLog(@"___%@",strTime);                [_timeBtn setTitle:[NSString stringWithFormat:@"%@秒后重新发送",strTime] forState:UIControlStateNormal];                _timeBtn.userInteractionEnabled = NO;            });        }        timeout-- ;    });    dispatch_resume(timer);}